The incidence of microbial infections (e.g., mycobacterial, fungal, and protozoal infections) in the immunocompromised population has significantly increased over the past several years. In particular, Candida species, especially Candida albicans, are often significant pathogens in patients infected with human immunodeficiency virus (HIV). Another pathogen, Pneumocystis carinii, causes a form of pneumonia (PCP) that is believed to be one of the leading causes of death in patients suffering from AIDS. Further, Human African trypanosomiasis (HAT) has reemerged as a threat to over 60 million people. Current estimates are that between 350,000 and 450,000 people are infected. Other severe and life-threatening microbial infections are caused by Mycobacterium tuberculosis, Aspergillus spp., Crypotosporidium parvum, Giardia lamblia, Plasmodium spp., Toxoplasma gondii, Fusarium solani, and Cryptococcus neoformans. 
The antimicrobial properties of dicationic molecules have been studied since the 1930's. Compounds of this type have typically utilized amidine groups as the cationic moieties, and their activities against a number of pathogens including Cryptosporidium parvum, Giardia lamblia, Leishmania spp., Plasmodium spp., Pneumocystis carinii, Toxoplasma gondii, Trypanosoma spp., Candida albicans, Aspergillus spp. and Cryptococcus neoformans have been reported. See, e.g., King, H. et al., Ann. Trop. Med. Parasitol. 1938, 32, 177-192; Blagburn, B. L. et al., Antimicrob. Agents Chemother. 1991, 35, 1520-1523; Bell, C. A. et al., Antimicrob. Agents Chemother. 1991, 35, 1099-1107; Bell, C. A. et al., Antimicrob. Agents Chemother. 1990, 34, 1381-1386; Kirk, R. et al., Ann. Trop. Med. Parastiol. 1940, 34, 181-197; Fulton, J. D. Ann. Trop. Med. Parasitol. 1940, 34, 53-66; Ivady, V. G. et al., Monatschr. Kinderheilkd. 1958, 106, 10-14; Boykin, D. W. et al., J. Med. Chem. 1995, 38, 912-916; Boykin, D. W. et al., J. Med. Chem. 1998, 41, 124-129; Francesconi, I. et al., J. Med. Chem. 1999, 42, 2260-2265; Lindsay, D. S. et al., Antimicrob. Agents Chemother. 1991, 35, 1914-1916; Lourie, E. M. et al., Ann. Trop. Med. Parasitol. 1939, 33, 289-304; Lourie, E. M. et al., Ann. Trop. Med. Parasitol. 1939, 33, 305-312; Das, B. P. et al., J. Med. Chem. 1976, 20, 531-536; Del Poeta, M. et al., J. Antimicrob. Chemother. 1999, 44, 223-228; Del Poeta, M. et al., Antimicrob. Agents Chemother. 1998, 42, 2495-2502; Del Poeta, M. et al., Anitmicrob. Agents Chemother. 1998, 42, 2503-2510.
Despite the broad range of activity exhibited by diamidines, only one compound of this chemical type, pentamidine, has seen significant clinical use. Pentiamidine has been used clinically against African trypanosomiasis, antimony-resistant leishmaniasis, and P. carinii pneumonia. See, e.g., Apted, F. I. C., Pharmacol. Ther. 1980, 11, 391-413; Bryceson, A. D. M. et al., Trans. Roy. Soc. Trop. Med. Hyg. 1985, 79, 705-714; Hughes, W. T. et al., Antimicrob. Agents Chemother. 1974, 5, 289-293.
Thus, there continues to be a need for improvement in the art for additional compounds having desirable anti-microbial activity, whether against the representative pathogens referenced above or against other pathogens.